Species-specific trophic enrichment factor of stable nitrogen and carbon isotopes in fish otolith organic matter

Context. Although stable carbon (delta C-13) and nitrogen (delta N-15) isotopes are widely used to study feeding ecology, the use of these isotopes in otolith organic matter to assess the diet of fishes is delta C-13 delta(15)Nrarely investigated. Aim. This study evaluated the relationship of and values among muscle, otolith organic matter and diet. The samples were analysed using an elemental analyzer connected to isotope-ratio mass spectrometry. Key results. The delta N-15 values were highest in muscle followed by otoliths, diet and plankton, although no significant difference in delta N-15 values was found between the otolith and diet for most of the samples. The fish collected from water reservoirs showed similar delta C-13 values between otolith and muscle, both of which were higher than the isotopic values of the fish diet. However, the farmed fishes showed small but significant difference in the delta C-13 values between muscle and otolith, which reflects diet change or commercial diet containing a mixture of different food items. Conclusion. Otolith delta N-15 value can provide information about fish diet and the otolith delta C-13 value can act as a good proxy of muscle delta C-13 composition in fish species. Implications. Otolith delta N-15 and delta C-13 values can faithfully reflect the trophic position and feeding behaviours of fish.